0.3.1

Fix recurrence calculations across daylight-saving transitions and skipped calendar dates.

• Preserve weekly schedules across timezone transitions.
• Preserve monthly recurrence times when month boundaries cross daylight-saving gaps.
• Continue monthly repeats past skipped dates without changing their frequency.
• Reject weekday occurrences that normalize to the wrong weekday.

Validation: All 66 tests pass.

Full Changelog: 0.3.0...0.3.1